This research falls within a broad effort to decode the program by which the human visual system processes the pattern of light in the retinal image in order to determine the white, gray of black level of surfaces within the field of view. It is generally accepted that perceived surface gray levels are based on relative light intensities extracted from intensity gradients in the retinal image, but little is known about how these relative intensities are anchored, that is, processed to yield the specific shades of gray that we see. For instance, in many scenes the visual system automatically treats the highest intensity as white. This can be demonstrated under the simplest conditions by placing an observer's head inside a large dome, half of the interior of which is painted black and half of which is painted gray. The gray part will appear white and the black part will appear gray, consistent with highest-intensity-as-white rule. But if an observer's head is placed within a uniformly painted black dome containing a white disk at its center, the black dome appears white and the disk appears luminous. This indicates a rule by which white is assigned tot eh surrounding region, not to the highest intensity. Human observers will be placed in a variety of visual environments, chosen to distinguish different potential anchoring rules. These will include simple patterns on large plastic domes that completely surround the viewer, more complex lab displays, computer simulated displays, and on-site natural scenes. The perceived shade of gray of each surface in the display will be obtained by having naive observers make matches using a gray scale. These values will be analyzed to determine what rule they represent. Analysis of how the anchoring rules change as the visual field becomes increasingly complex is expected to fill an important gap in the modelling of surface color perception. An understanding of how the visual system determines surface colors in general will provide an essential framework for understanding certain forms of visual impairment provide an essential framework for understanding certain forms of visual impairment.